Charges in the passivation layers and on the top passivation surface over a junction termination edge for high voltage power devices have been found to cause severe reliability failure (Hamza Yilmaz, “Optimization and Surface Charge Sensitivity of High Voltage Blocking Structures with Shallow Junction”, IEEE Trans. Electron Devices, Vol 38, No. 7, P1666-1675, July 1991; John W. Osenbach and W. Knolle, “Semi-Insulating Silicon Nitride (SinSiN) as a Resistive Field Shield”, IEEE Trans. Electron Devices, Vol. 37, No. 6, pp 1522-1528, June 1990; Jack Korec and Raban Held, “Comparison of DMSO/IGBT-Compatible High-Voltage Termination Structures and Passivation Techniques”, IEEE Trans. Electron Devices, Vol. 40, No. 10, pp 1845-1554, October 1993). Semi-Insulating Silicon Nitride or Semi-Insulating Polycrystalline Silicon (SIPOS) has been used to reduce or shield the charges in high voltage power devices (Osenbach and Knolle, supra; T. Matsushita et al, “Highly Reliable High-Voltage Transistors by Use of SIPOS Process”, IEEE Trans. Electron Devices, Vol ED-23, No. 8, pp 826-830, August 1976).
However, these methods still suffer from a number of problems. They couldn't screen all the charge effects on the Silicon due to their low conductivity. The devices are still failing or unstable after the high temperature and high voltage stress. For Semi-Insulating Silicon Nitride, although the film conductivity can be increased through lowering NH3/SiH4 ratio, the conductivity is limited in the range of 10−10 (Ω-cm)−1 order (Osenbach and Knolle, supra), and the refractive index would be increased. Thus the stress for the film can also be increased (B. Kim et al., “Use of Neural Network to Control a Refractive Index of SiN Film Deposited by Plasma Enhanced Chemical Vapor Deposition”, Plasma Chemistry and Plasma Processing, Vol 24, No. 1, March 2004) and more Si—H bonds can be produced. During high temperature reversed bias (HTRB) stress, some of the Si—H and N—H bonds in the film can be broken, and form the new charges and trapped centers. For SIPOS, some of the problems are the excessive leakage current and its extreme reactivity with humid environments (Osenbach and Knolle, supra). The breakdown voltage has been seriously degraded after HTRB stress.
Therefore, it can be appreciated that a new passivation method to improve the stability of the breakdown voltage would be highly desirable.